When opto-electronic devices such as those mentioned above are fixed to a substrate, such as a silicon waferboard substrate, during fabrication of an overall assembly, the devices must be precisely aligned with respect to each other in order for the overall combined packaged assembly to operate properly. That is, if both a semiconductor laser device and an optical fiber are to be placed on the same substrate so that they interact with each other, the optical axis of the laser must be precisely aligned with that of the optical fiber, so that a laser beam emitted from the semiconductor laser will be precisely guided in the intended direction by the optical fiber. In addition, the spacing between each device must also be precisely set during fabrication.
Two methods of obtaining such alignment of devices are well known in the art. The first is called active alignment because, in the above example of a semiconductor laser being aligned to an optical fiber, the laser is turned on during the alignment process. According to the active alignment method, the light beam emanating from the laser is passed through the fiber and a photodetector placed at the other end of the fiber monitors the amount of light passing through the fiber as the laser is iteratively moved with respect to the fiber, in three axial lateral dimensions (x, y, z) and in three axial rotational directions (rotation about each of axes x, y, z). Optionally, the fiber can be iteratively moved with respect to the laser. That is, the positional relationship between the laser and the fiber is continuously altered until the photodetector detects an optimal alignment of the beam, indicated by maximum detected intensity. Once the optimal alignment is achieved, both the laser and the fiber are fixed into place on the substrate by adding a bonding agent, such as solder, to junction points between each device and the substrate.
Since this iterative process is required in order to precisely align the optical or opto-electronic devices, the active alignment technique is quite time-consuming and thus results in high fabrication costs. Further, many complex multiple optical beam devices (such as a semiconductor laser array which outputs a plurality of laser beams side-by-side) are nearly impossible to practically package using this technique, since alignment of one beam can affect the others, thus requiring that each beam be monitored while the alignment of each beam is iteratively adjusted.
The second known alignment technique was developed by GTE.RTM. Laboratories as an improvement over the active alignment technique, and is described in U.S. Pat. No. 5,436,996 herein incorporated by reference. This second technique is called a passive alignment technique, because during alignment, taking the laser/optical fiber example, the laser is turned off. The substrate upon which the laser and optical fiber will be affixed, and the laser itself, are formed with micromachined surfaces (e.g., pedestal stops, standoffs and alignment notches). For example, alignment notches would be formed in the laser device in order to aid in the lateral alignment of the active region of the laser device. In this way, the micromachined surface of the laser can be easily fit into its predetermined place on the substrate by an interlocking of the mating micromachined surfaces of the laser and substrate. The optical fiber sits in a V-groove already etched into the substrate.
The passive alignment technique greatly lowers the total time required for obtaining the optimal alignment of optical or opto-electronic devices, since the specific locations for each device on the substrate are predetermined and accounted for by micromachining during manufacture of each device and of the substrate. However, while it is possible for an assembly manufacturer (i.e, a manufacturer of the overall integrated package assembly of the substrate and the mounted devices) to have good control over the micromachining of the substrate, it is difficult for the assembly manufacturer to maintain such control over the micromachining of various devices. That is, each device is potentially made by a different device manufacturer and the assembly manufacturer would have to make sure that each device manufacturer micromachines its device in exactly the required manner.
Thus, there are disadvantages to both well known alignment methods and a satisfactory alignment method which does not suffer from such disadvantages was not known in the prior art. For this reason, the formation of integrated packages has become quite difficult. In the past, such difficulty could be tolerated, since one of such integrated packages would be shared amongst thousands of telephone fiber optic communications customers. However, the need for quickly and accurately aligning optical or opto-electronic devices on a substrate has become more and more important recently as telephone companies begin extending optical fiber networks directly to the home.